EP3637420A1 - Procédé de propagation de partition de domaine magnétique dans des dispositifs magnétiques - Google Patents

Procédé de propagation de partition de domaine magnétique dans des dispositifs magnétiques Download PDF

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Publication number
EP3637420A1
EP3637420A1 EP19202117.8A EP19202117A EP3637420A1 EP 3637420 A1 EP3637420 A1 EP 3637420A1 EP 19202117 A EP19202117 A EP 19202117A EP 3637420 A1 EP3637420 A1 EP 3637420A1
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EP
European Patent Office
Prior art keywords
magnetic
bus
magnetic bus
output
buses
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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EP19202117.8A
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German (de)
English (en)
Inventor
Mr. Adrien Vaysset
Mr. Zografos Odysseas
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Katholieke Universiteit Leuven
Interuniversitair Microelektronica Centrum vzw IMEC
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Katholieke Universiteit Leuven
Interuniversitair Microelektronica Centrum vzw IMEC
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Priority claimed from US16/155,158 external-priority patent/US10593414B2/en
Application filed by Katholieke Universiteit Leuven, Interuniversitair Microelektronica Centrum vzw IMEC filed Critical Katholieke Universiteit Leuven
Publication of EP3637420A1 publication Critical patent/EP3637420A1/fr
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
    • G11C11/14—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using thin-film elements
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
    • G11C11/16—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect
    • G11C11/165—Auxiliary circuits
    • G11C11/1675—Writing or programming circuits or methods
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C19/00—Digital stores in which the information is moved stepwise, e.g. shift registers
    • G11C19/02—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C19/00—Digital stores in which the information is moved stepwise, e.g. shift registers
    • G11C19/02—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements
    • G11C19/08—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure
    • G11C19/0808—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure using magnetic domain propagation
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C19/00—Digital stores in which the information is moved stepwise, e.g. shift registers
    • G11C19/02—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements
    • G11C19/08—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure
    • G11C19/0808—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure using magnetic domain propagation
    • G11C19/0841—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure using magnetic domain propagation using electric current

Definitions

  • the invention generally relates to magnetic devices, and more particularly to magnetic devices configured to generate a stream of domain walls.
  • Some storage devices including hard-disk drives and magnetic random access memory (MRAM) devices utilize magnetic domains to store information.
  • MRAM magnetic random access memory
  • Some storage devices including hard-disk drives and magnetic random access memory (MRAM) devices utilize magnetic domains to store information.
  • magnetic domains When such magnetic domains are formed in a magnetic strip, they can be shifted along the magnetic strip, for example by applying a spin transfer torque (STT) or spin-orbit torque (SOT).
  • STT spin transfer torque
  • SOT spin-orbit torque
  • This induced domain wall (DW) motion may have various applications, including applications in logic and memory devices.
  • a domain wall memory device e.g., memory device referred to as racetrack memory device
  • racetrack memory device is a non-volatile memory device that can potentially provide high storage densities, e.g., densities comparable to those of conventional magnetic disk drives, as well as providing high data throughput in read and write operations, e.g., throughputs including read and write speeds that are comparable to or faster those of some dynamic random access memory (DRAM) devices.
  • DRAM dynamic random access memory
  • a spin-coherent electric current may be used to move a sequence of magnetic domains through a substrate, e.g., along a magnetic bus, e.g., along a permalloy wire.
  • Read/write elements may be provided at predetermined positions near the substrate to encode or decode the sequence of magnetic domains in the form of a data stream.
  • high bit densities can be achieved by using state-of-the-art spintronic devices to detect and/or manipulate particularly small magnetic domains.
  • a domain wall memory may, for example, comprise a plurality of flat magnetic buses, e.g., flat wires, arranged in a grid with read and write heads arranged nearby.
  • a U-shaped wire may be arranged vertically over a read/write head on an underlying substrate, e.g., to provide a small footprint on the substrate on which the read/write head is provided.
  • Such a domain wall memory is described in United States Patent No. 6,834,005 , which discloses a shift register that uses the inherent, natural properties of domain walls in magnetic materials to store data.
  • This shift register uses spin electronics without changing the physical nature of its constituent materials.
  • the shift register comprises a fine track or strip of magnetic materials. Information is stored as domain walls in the track.
  • An electric current can be applied to the track to move the magnetic moments along the track past a reading or writing device, e.g., a magnetic read/write head.
  • a current passed across the domain wall may move the domain wall in the direction of the current flow. As the electrons pass through a domain, they can become spin polarized.
  • Domain wall motion may be typically created by the application of a magnetic field.
  • This approach has some disadvantages, including a relatively large current that may be needed to generate the magnetic field, which may render the devices difficult to scale down.
  • Phung et al. disclosed, in "Highly efficient in-line magnetic domain wall injector", Nano Letters 15 (2), pp. 835-841 , a method of injecting a domain wall without using an external magnetic field. In this method, a small in-plane region is created at the end of a perpendicularly magnetized strip. Then, an in-plane current is applied. The spin polarization induced by the in-plane region generates a spin torque on the perpendicular magnetization nearby.
  • a domain wall is thus injected without using an external magnetic field.
  • the in-plane region may for example be created by ion irradiation, voltage-controlled anisotropy or ion etching.
  • ion irradiation may be precisely controlled to avoid large variability between devices.
  • additional constraints may be introduced to the process flow by such process steps, and an increase in cost may be implied by these process steps.
  • domain walls can be injected in a magnetized material without requiring an external magnetic field during operation, e.g., without relying on Oersted field.
  • the application of a field to nucleate domain walls may not be used to write data to a racetrack memory after the input domains have been initialized, according to embodiments.
  • domain walls can be injected in a perpendicularly magnetized material without requiring an in-plane magnetized region in the perpendicularly magnetized material.
  • domain walls can be injected in a magnetized material in a simple to implement and efficient manner.
  • any sequence of bits e.g., a freely selectable sequence, can be converted into a stream of magnetic domains on a racetrack memory.
  • a low- current and energy efficient method of generating a stream of magnetic domains on a racetrack memory is provided. Additionally, instead of nucleating a new domain wall for each magnetic domain transition in a data sequence, e.g., a freely selectable bit sequence, being written to a racetrack memory, a previously initialized domain wall can be expanded and reused, thus achieving improved energy efficiency and/or allowing a low- current implementation.
  • the invention provides a method of generating a stream of domain walls propagating along an output magnetic bus.
  • the method comprises providing a device that comprises a magnetic propagation layer.
  • the magnetic propagation layer comprises a plurality of magnetic buses for guiding propagating magnetic domain walls along a longitudinal direction, or in a direction perpendicular to layer normal direction, of the magnetic bus.
  • the magnetic propagation layer further comprises a region in which the magnetic buses converge and are joined together. This region may be a convex region. This region may be an intersection in which the plurality of magnetic buses converge and are joined together.
  • the plurality of magnetic buses comprises at least a first magnetic bus and a second magnetic bus having an opposite magnetization component with respect to each other such that a domain wall separating the opposite magnetization states is pinned in the region in which the plurality of magnetic buses converge and are joined together.
  • the plurality of magnetic buses further comprises the output magnetic bus serving as an output for the stream of domain walls.
  • the method also comprises generating the stream of domain walls propagating along the output magnetic bus by applying spin orbit torques and/or spin transfer torques to the pinned domain wall such as to alternate the pinned domain wall between two stable configurations, in which each stable configuration corresponds to a different magnetization state of the output magnetic bus in at least a region where the output magnetic bus is joined to the region in which the plurality of magnetic buses converge and are joined together.
  • a method in accordance with embodiments of the invention may further comprise initializing at least the first magnetic bus and the second magnetic bus of the plurality of magnetic buses in the opposite magnetization states with respect to each other.
  • the step of initializing may further comprise initializing at least a further magnetic bus to either of the opposite magnetization states.
  • the step of applying the spin transfer torque may comprise applying an in-plane current between the output magnetic bus, on one hand, and the first magnetic bus and/or the second magnetic bus, on the other hand, such as to establish at least one current path through the region, in which the plurality of magnetic buses converge and are joined together, toward the output magnetic bus.
  • the step of applying the in-plane current may comprise selecting either the first magnetic bus or the second magnetic bus for injecting the in-plane current, in which this selection may be determined by a data bit in a data bit sequence for converting into the stream of domain walls.
  • the step of applying the in-plane current may comprise applying a first in-plane current between the output magnetic bus and the first magnetic bus and simultaneously applying a second in-plane current between the output magnetic bus and the second magnetic bus, to create an oscillation between the two stable configurations, thereby periodically generating a domain wall between opposite magnetization states that propagates down the output magnetic bus.
  • providing the device may comprise providing the device in which the first magnetic bus and the second magnetic bus are tapered, e.g., have a decreasing width in the direction toward the region in which the plurality of magnetic buses converge and are joined together.
  • a method in accordance with embodiments of the invention may further comprise using the output magnetic bus as a racetrack data memory.
  • providing the device may comprise providing the device wherein the region in which the plurality of magnetic buses converge and are joined together has a convex shape, e.g., a convex polygonal shape.
  • providing the device may comprise providing the device, wherein each edge of the convex shape, e.g., of the convex polygonal shape, is formed by an end region of a corresponding magnetic bus of the plurality of magnetic buses and wherein each corner of the convex shape is shared with two adjacent magnetic buses of the plurality of magnetic buses.
  • providing the device may comprise providing the device wherein a plurality of configurations of locally minimal energy for a domain wall correspond to line segments connecting corners of the region in which the plurality of magnetic buses converge and are joined together.
  • the domain wall in the region, in which the plurality of magnetic buses converge and are joined together may alternate between the two stable configurations, wherein each stable configuration corresponds to one of the plurality of configurations of locally minimal energy.
  • providing the device may comprise providing the device wherein the plurality of magnetic buses is arranged in a star configuration around the region in which the plurality of magnetic buses converge and are joined together, each magnetic bus extending radially outward from the region in which the plurality of magnetic buses converge and are joined together.
  • providing the device may comprise providing the device wherein the plurality of magnetic buses is arranged to form a triangular shape of three magnetic buses extending outward from a triangular region in which the plurality of magnetic buses converge and are joined together.
  • providing the device may comprise providing the device wherein the plurality of magnetic buses is arranged to form a cross shape of four magnetic buses extending outward from a square region in which the plurality of magnetic buses converge and are joined together.
  • the invention relates to a method of generating a stream of domain walls propagating along a magnetic bus, e.g., for recording data in a domain wall memory, e.g., for writing, erasing or programming data to a domain wall racetrack memory.
  • the method comprises providing a device comprising a magnetic propagation layer that comprises a plurality of magnetic buses for guiding propagating magnetic domain walls along a longitudinal direction of the magnetic bus.
  • the magnetic propagation layer comprises a region, e.g., an adjoining region, in which the plurality of magnetic buses converge and are joined together, e.g., a central region in which the plurality of magnetic buses converge and are joined together.
  • a central region refers to a region of convergence of the magnetic buses in this convex region, and does not necessarily refer to or limit to a geometrically central location of the convex region.
  • a convex region refers to a polygonal region having each of the interior angles that are less than 180°.
  • the central region may, for example, be an intersection in which the plurality of magnetic buses converge and are joined together, which may or may not be formed at a geometric central location.
  • the plurality of magnetic buses comprises at least a first magnetic bus and a second magnetic bus having an opposite magnetization orientation with respect to each other.
  • the first and second magnetic buses having the opposite magnetization orientation with respect to each other can have magnetization vectors, e.g., average or net magnetization vectors, that form an angle in the range of about 135° to about 180° with respect to each other, in the range of 160° to 180°, in the range of about 170° to about 180°, or in a range defined by any of these values, e.g., substantially about 180°.
  • a domain wall separating the opposite magnetization states is pinned in the central region.
  • the plurality of magnetic buses further comprises an output magnetic bus, e.g., a third magnetic bus, serving as an output for the stream of domain walls.
  • a pinned domain wall refers to the domain wall being in a local energy minimum, e.g., due to a configuration of the domain wall in the region in which the plurality of magnetic buses converge and are joined together that is energetically lower with respect to other configurations in a local neighborhood of this configuration.
  • the method also comprises generating a stream of domain walls that propagate along the output magnetic bus by applying spin orbit torques and/or spin transfer torques to the pinned domain wall such as to alternate, e.g., to switch, the pinned domain wall between two stable configurations, in which each stable configuration corresponds to a different magnetization state of the output magnetic bus.
  • This method 100 is adapted for generating a stream of domain walls propagating along a magnetic bus, i.e. along the output magnetic bus referred to further hereinbelow.
  • the method 100 comprises providing 101 a device, e.g., a domain wall injector device, comprising a magnetic propagation layer.
  • a device e.g., a domain wall injector device
  • the magnetic propagation layer may comprise a magnetic material adapted for allowing the propagation of magnetic domain walls, including a ferromagnetic and/or antiferromagnetic material, or a composite material formed by constituent ferromagnetic and/or antiferromagnetic materials.
  • the magnetic propagation layer may be perpendicularly or in-plane magnetized with respect to a lateral direction parallel to a major surface of the magnetic propagation layer or a substrate.
  • the magnetic propagation layer comprises a plurality of magnetic buses 11, 12, and 13 for guiding propagating magnetic domain walls along a longitudinal direction or an in-plane direction of the magnetic bus.
  • the magnetic buses 11, 12, and 13 are configured as elongated magnetized structures, such as strips or wires, e.g., nanostrips or nanowires, formed in the magnetic propagation layer.
  • the magnetic propagation layer also comprises a central region 15 in which the plurality of magnetic buses converge and are joined together.
  • the term central region refers to a region that serves as a junction connecting the magnetic buses, and thus refers to a topologically central region with respect to the plurality of magnetic buses. That is, a central region does not necessarily refer to or limit to a geometrically central location.
  • the central region 15 has a convex shape, such as a regular polygonal shape.
  • each edge of such convex shape e.g., regular polygonal shape
  • Each corner of such convex shape, e.g., regular polygonal shape may be shared with two adjacent magnetic buses of the plurality of magnetic buses.
  • the plurality of magnetic buses may be arranged in a star configuration around the central region, e.g., such that each magnetic bus extends radially outward from the central region, for example to form a cross shape of four magnetic buses extending outward from a square central region, such as shown in FIG.
  • the device may be formed by two magnetic strips crossing each other in the central region. It may be an advantage of such embodiments that arranging the magnetic buses in a cross pattern may be efficient and easy to manufacture.
  • the plurality of magnetic buses may also be arranged such as to form a triangular shape of three magnetic buses extending outward from a triangular central region, e.g., as shown in FIG. 2 .
  • the triangular central region may be an isosceles triangular central region, e.g., an equilateral triangular central region.
  • the magnetic buses may be uniformly angularly spaced around the central region, e.g., as illustrated by the triangular configuration of FIG. 2 and the cross-shaped configuration of FIG. 6 , or may be non-uniformly spaced around the central region, e.g., such as the T-junction configuration shown in FIG. 18 or the acute angle junction shown in FIG. 19 .
  • At least two, e.g., a first magnetic bus 11 and a second magnetic bus 12, of the plurality of magnetic buses have different, e.g., opposite, magnetization orientations, e.g., opposite transverse magnetization orientations or opposite in-plane magnetization orientations, with respect to each other such that a domain wall 16, separating the opposite magnetization states of the first magnetic bus 11 and the second magnetic bus 12, is pinned in the central region 15.
  • the plurality of magnetic buses also comprises an output magnetic bus 13 serving as an output for the stream of domain walls.
  • At least one magnetic bus e.g., at least one input magnetic bus such as one of the first and second magnetic buses 11, 12, different from the output magnetic bus 13, may have an 'UP' transverse magnetization state
  • at least one magnetic bus e.g., at least one input magnetic bus such as the other of the first and second magnetic buses 11, 12, different from the output magnetic bus 13, may have a 'DOWN' transverse magnetization state.
  • a first magnetic bus 11 and a second magnetic bus 12 of the plurality of magnetic buses may have different or opposite in-plane magnetization states with respect to each other such that a domain wall 16, separating the magnetization states of the first magnetic bus 11 and the second magnetic bus 12, is pinned in the central region 15.
  • a first magnetic bus 11 may have a +x in-plane magnetization component
  • a second magnetic bus 12 may have a -x in-plane magnetization component.
  • the in-plane magnetization states may have a component, e.g., an x-component, of opposite signs, e.g., -x and +x, with respect to each other.
  • this component may be substantially oriented along the orientation of the output magnetic bus 13.
  • each of the first magnetic bus and the second magnetic bus may be oriented at a small angle with respect to this orientation, e.g. an angle in the range of 5° to 45°, in the range of 5° to 30°, in the range of 10° to 20°, or in a range defined by any of these values.
  • the central region 15 may have a convex or a polygonal shape, and each corner of this convex shape may lie in between two adjacent magnetic buses of the plurality of magnetic buses.
  • a plurality of configurations of local energy minima for a propagating domain wall may correspond to line segments 19 connecting corners of the central region, e.g., to edges and/or diagonals of the convex shape, such as shown in FIG. 6 .
  • the device may be preset or initialized in a magnetic configuration such that a domain wall is present in the central region. This domain wall may be stable when substantially aligned along one of the diagonals or edges of the convex or polygonal shape. For example, in the example shown in FIG.
  • a stable configuration of the domain wall may correspond to the edge 21, where the first magnetic bus 11 transitions into the central region 15, if the output magnetic bus 13 and the second magnetic bus 12 have the same magnetic orientation.
  • Another stable configuration may correspond to the edge 22, where the second magnetic bus 12 transitions into the central region 15, if the output magnetic bus 13 and the first magnetic bus 11 have the same magnetic orientation.
  • the stable configurations may correspond to pinning sites for domain walls, where a magnetic domain wall may be pinned, e.g., "trapped", in a local energy minimum until it is released by a driving force, e.g., by a torque exerted on the domain wall.
  • first magnetic bus 11 and the second magnetic bus 12 may be tapered, e.g., may have a decreasing width in the direction toward the central region, such as shown in FIG. 20 .
  • the stable configurations referred to hereinabove may be characterized by a sharp and well-defined local energy minimum.
  • the tapered shape may cause a steeper energy gradient with respect to displacements of the stable configuration, e.g., of the pinned domain wall in the central region, as compared to such energy gradient in the absence of the tapered shape.
  • the energy cost of this virtual displacement may be higher than in the case where the magnetic bus would have a constant width and/or a constant cross-section.
  • a pinned domain wall may be better constrained in the central region, e.g., may be prevented from wandering into an input magnetic bus 11, 12, and 18 due to the energetically less favorable configuration corresponding to a wider domain wall cross-section in the magnetic bus than in the stable configuration in the central region.
  • the method 100 may comprise initializing 102 at least the first magnetic bus 11 and the second magnetic bus 12 of the plurality of magnetic buses in opposite magnetization states with respect to each other, such that a domain wall 16, separating the opposite magnetization states of the first magnetic bus 11 and the second magnetic bus 12, is pinned in the central region 15.
  • At least a further magnetic bus 18 may also be initialized to either magnetization state when the device is configured according to FIGS. 6-16 .
  • At least one magnetic bus e.g., at least one input magnetic bus, e.g., one of the first and second magnetic buses 11, 12, different from the output magnetic bus 13, may be initialized to an 'UP' transverse magnetization state
  • at least one input magnetic bus e.g., the other of the first and second magnetic buses 11, 12, different from the output magnetic bus 13
  • a suitable method may be used, e.g., magnetic fields may be applied to induce the different magnetization states.
  • each magnetic domain in such stream of magnetic domains may be generated as having an arbitrary length.
  • the device may be preset or initialized in a magnetic configuration such that a domain wall is present in the central region.
  • This domain wall may be stable when substantially aligned along one of the diagonals or edges of the convex shape.
  • this stable configuration may correspond to a diagonal of the square central region defined by central edges of each of the magnetic buses 11, 12, 13 and 18, if the further magnetic bus 18 has a first magnetization state corresponding to that of either the first 11 or the second magnetic bus 12, and the output magnetic bus 13 has a second magnetization state corresponding to that of the other one of the first or the second magnetic bus.
  • a stable configuration may correspond to an edge of the square region if three of the four exemplary magnetic buses share the same magnetization state, and the fourth one is in the opposite magnetization state.
  • the method 100 further comprises generating 105 a stream of domain walls that propagate along the output magnetic bus 13 by applying 106 spin orbit torques and/or spin transfer torques to the pinned domain wall such as to switch 107 the pinned domain wall between two stable configurations, in which each stable configuration corresponds to a different transverse magnetization state of the output magnetic bus.
  • the output magnetic bus 13 has an initial magnetization corresponding to that of the second magnetic bus 12, while the first magnetic bus 11 has an opposite magnetization.
  • Applying a spin transfer torque may comprise applying a current between the output magnetic bus 13, on one hand, and the first magnetic bus 11 and/or the second magnetic bus 12, on the other hand.
  • generating 105 the stream of domain walls may comprise applying currents along at least two different current paths, e.g., a first path between the first magnetic bus 11 and the output magnetic bus 13 and a second path between the second magnetic bus 12 and the output magnetic bus 13.
  • the magnetization state of the magnetic domain injected into the output magnetic bus 13, e.g., an 'UP' or a 'DOWN' domain or a '-x' or '+x' domain may thus be determined by whether a current is applied along the first current path or the second current path. For example, applying a current along the first current path may inject an 'UP' domain into the output bus, while applying a current along the second current path may inject a 'DOWN' domain into the output bus.
  • Each of the current paths may share a common segment along the output bus, e.g., due to a source or sink in the output bus that is shared by both current paths, such that a current applied along either current path may be adapted for propagating a sequence of magnetic domains via the output magnetic bus, e.g., away from the central region and through the output magnetic bus.
  • an efficient spin transfer torque may be induced by applying an in-plane current
  • other methods for generating a spin transfer torque or spin orbit torque on domain walls could be utilized within the context of the present disclosure.
  • a spin-orbit torque may be generated to propel the domain wall, which may be advantageously energy efficient.
  • high domain wall propagation speeds may be achieved by combining the application of spin orbit torques with a composite magnetic layer structure of the magnetized propagation layer.
  • an electron flow e- may be applied such that electrons flow from the first magnetic bus 11 to the output magnetic bus 13, as illustrated in FIG. 3 , e.g., a current I may be applied from the output magnetic bus 13 to the first magnetic bus 11.
  • FIG. 2 to FIG. 5 show, progressively, the evolution of the domain wall 16 when such current is applied.
  • the applied current may exert a driving force on the domain wall 16, such that the domain wall eventually splits to form a further domain wall 17 propagating along the output magnetic bus 13, while the domain wall 16 remains in the central region, as shown in FIG. 4 .
  • the injected current may move the domain wall from its initial stable position, e.g., shown in FIG. 2 , gradually expand the domain wall, e.g., shown in FIG. 3 , until it splits into two parts, e.g., as shown in FIG. 4 .
  • One part may remain at the junction to be pinned at the other stable position, while the other part of the domain wall may propagate into the output magnetic bus. Therefore, the propagation through the output magnetic bus 13 of the further domain wall 17 that was injected into the output magnetic bus 13 may advantageously also be driven by the same current that is applied to split the further domain wall 17 off the domain wall 16 is the central region.
  • the domain wall 16 in the central region may then reach the other stable configuration.
  • the first stable configuration may correspond to a magnetization state of the output magnetic bus 13, e.g., at least where it is joined to the central region, that corresponds to that of the second magnetic bus 12, as shown in FIG. 2
  • the second stable configuration may correspond to a magnetization state of the output magnetic bus 13, e.g., at least where it is joined to the central region, that corresponds to that of the first magnetic bus 11, e.g., as shown in FIG. 5 .
  • Applying the spin orbit torque and/or spin transfer torque may comprise applying a current between the output magnetic bus 13, on one hand, and the first magnetic bus 11 and/or the second magnetic bus 12, on the other hand.
  • an in-plane current may be injected in the first and/or second magnetic bus such as to establish a current path or current paths through the central region toward the output magnetic bus 13, or, alternatively, from the output magnetic bus to the first and/or second magnetic bus for the opposite current sense.
  • Such in-plane current may generate a spin torque on the magnetization, e.g., electrons flowing toward the domain wall to push the domain forward (or, equivalently an opposite polarity current may be applied to push the domain wall forward, depending on the material properties of the magnetic propagation layer in which the magnetic buses are formed).
  • applying this current may comprise selecting the first magnetic bus 11 or the second magnetic bus 12 to inject the current, in which this selection is determined by a data bit in a data bit sequence to convert into the stream of domain walls to send propagating along the output magnetic bus 13, e.g., determined by a next data bit in the sequence to be sequentially encoded as magnetic domains transmitted via the output magnetic bus.
  • the method may be used to selectively inject magnetic domains into the output magnetic bus, which, for example, may be an input for a spintronic logic device or a racetrack in a racetrack memory. If a current is injected into the first magnetic bus, e.g., one of magnetic buses 11, 12, 18, a domain having the same magnetization as the first magnetic bus may be injected into the output magnetic bus 13, while if a current is injected into the second magnetic bus, e.g., another one of magnetic buses 11, 12, 18, a domain having the same magnetization as the second magnetic bus may be injected into the output magnetic bus 13.
  • any data sequence can be easily encoded in a stream of 'UP' and 'DOWN' magnetization domains by a synchronized application of the current to the first and second magnetic bus.
  • opposite torques may also be exerted simultaneously on a domain wall, in order to create an oscillation between the two stable configurations.
  • a current may be applied between the output magnetic bus 13, on one hand, and the first magnetic bus 11 and the second magnetic bus 12 (and optionally any or each further magnetic bus 18) on the other hand, such as shown in FIG. 6 .
  • FIG. 6 For example, in the example shown in FIG.
  • the first magnetic bus 11 and the further magnetic bus 18 may be preset or initialized in a first magnetization state U, e.g., a 'UP' magnetization state
  • the second magnetic bus 12 and the output magnetic bus 13 may be preset or initialized in a second magnetization state D different from the first magnetization state, e.g., a transverse 'DOWN' magnetization state.
  • the in-plane currents may generate a spin torque on the magnetization, e.g., electrons flowing toward the domain wall may push it forward. After a small displacement of the domain wall, the net torque may change sign due to the spatial distribution of current. Thus locally reversing the direction in which the domain wall moves.
  • These variations of torques may cause an oscillation when current is applied to both input arms.
  • the 'UP' domain may propagate to the output magnetic bus
  • the 'DOWN' domain may propagate to the output magnetic bus.
  • a domain wall may thus be injected when the orientation of the propagating domain changes.
  • the in-plane current may preferably be selectively applied to either input arm, in order to control the magnetic domain injection.
  • a single domain wall may be injected into the output magnetic bus 13.
  • the propagation of injected domain walls through the output magnetic bus 13 may advantageously also be driven by the same injected currents that generate the oscillation in the central region.
  • the method 100 may further comprise using 108 the generated stream of domain walls propagating along the output magnetic bus 13 to write data to a racetrack memory.
  • the method 100 may be applied for a write scheme for a racetrack memory.
  • the output magnetic bus may be a magnetic domain racetrack.
  • a magnetic device can include a first magnetic bus and second magnetic bus having controllable magnetization orientations.
  • FIG. 21 illustrates an exemplary magnetic device having magnetic buses with controllable magnetization orientations.
  • FIG. 21 illustrates magnetic device 2100, having a first magnetic bus 2111, a second magnetic bus 2112, and an output magnetic bus 2113.
  • the magnetic buses can be oriented, for example, as described above with respect to FIG. 2 , and may further include an adjoining region in which the magnetic buses converge.
  • magnetic device 2100 may be provided as part of a magnetic propagation layer.
  • Magnetic device 2100 may include a first input 2121 configured to control a magnetization orientation of first magnetic bus 2111 and a second input 2122 configured to control a magnetization orientation of second magnetic bus 2112.
  • the magnetization orientations of first magnetic bus 2111 and second magnetic bus 2112 can be controlled by applying spin orbit torques and/or spin transfer torques by way of first input 2121 and second input 2122 respectively.
  • the magnetization orientations of first magnetic bus 2111 and second magnetic bus 2112 can be controlled in other ways as well. In this fashion, first magnetic bus 2111 and second magnetic bus 2112 can each be oriented in two or more magnetic orientations.
  • first magnetic bus 2111 and second magnetic bus 2112 are depicted as being oriented in a 'DOWN' state.
  • a magnetization state of a domain wall injected into output magnetic bus 2113 may correspond to a logical '0' or '1.
  • a 'DOWN' magnetic state may correspond to a '0
  • an 'UP' magnetic state may correspond to a '1.
  • an injected domain wall can correspond to a '0' or a '1' based on which magnetic bus, first magnetic bus 2111 or second magnetic bus 2112, is selected, and based on the magnetic orientation of the magnetic bus at the time of selection.
  • output magnetic bus 2113 may provide a single output for multiple inputs that correspond to a '0' or a '1.
  • FIG. 21 provides an example of a magnetic device 2100 that operates as a multiplexer.
  • Magnetic device 2100 may serve as a logic element within a logic circuit.
  • first magnetic bus 2111, second magnetic bus 2112, and/or output magnetic bus 2113 may be connected to other portions of the logic circuit, allowing for a logic circuit to exist on the same magnetic propagation layer on which magnetic device 2100 is provided.
  • FIG. 22 illustrates another exemplary magnetic device having magnetic buses with controllable magnetization orientations.
  • Illustrated magnetic device 2200 includes first magnetic bus 2211, second magnetic bus 2212, and output magnetic bus 2213.
  • Magnetic device 2200 further includes a first input 2221 and second input 2222 which respectively control a magnetic orientation of first magnetic bus 2211 and second magnetic bus 2212.
  • inputs 2221 and 2222 may include a charge-to-spin converter.
  • inputs 2221 and/or 2222 can use a Magnetic Tunnel Junction, an SOT device, or a magnetoelectric cell to control the magnetic orientation of first magnetic buses 2211 and 2212.
  • Each charge-to-spin converter may include control terminals.
  • first input 2221 includes terminals 2231 (labelled 'A' in FIG.
  • second input 2222 includes terminals 2233 (labelled 'C') and 2234 (labelled 'D'). Applying current between terminals A 2231 and B 2232 or C 2233 and D 2234 will power a charge-to-spin conversion that controls the orientation of magnetic buses 2211 and 2212 respectively.
  • selecting first magnetic bus 2211 may include applying a current between terminal A 2231 or terminal B 2232 and output magnetic bus 2213.
  • selecting second magnetic bus 2212 may include applying a current between terminal C 2233 or terminal D 2234 and output magnetic bus 2213.
  • selection signal Such an applied current may be referred to as a "selection signal,” and may flow between first magnetic bus 2211 and output magnetic bus 2213 or between second magnetic bus 2212 and output magnetic bus 2213.
  • FIG. 23A and FIG. 23B illustrate generation of domain walls propagating down the output magnetic bus in a device as shown in FIG. 21 .
  • FIG. 23A shows magnetic device 2300 having a first magnetic bus, a second magnetic bus, and an output bus.
  • a selection signal 2302 is also depicted as being applied between the first magnetic bus and the output magnetic bus.
  • Selection signal 2302 can be, for example, a current applied between the first magnetic bus and the output bus.
  • FIG. 23A further illustrates a domain wall 2304, which propagates along the output magnetic bus as a result of selection signal 2302 being applied.
  • First input 2321 is depicted as controlling the first magnetic bus such that the first magnetic bus is in a 'DOWN' magnetic state.
  • Second input 2322 is depicted as controlling the second magnetic bus such that the second magnetic bus is also in an 'UP' magnetic state. Because selection signal 2302 is depicted as selecting the first magnetic input and because first input 2321 is in a 'DOWN' magnetic state, domain wall is also in a 'DOWN' magnetic state.
  • FIG. 23B depicts a domain wall 2308, which propagates along the output magnetic bus as a result of a second selection signal 2306 being applied between the second magnetic bus and the output magnetic bus.
  • First input 2321 is depicted as controlling the first magnetic bus such that the first magnetic bus is in a 'DOWN' magnetic state.
  • Second input 2322 is depicted as controlling the second magnetic bus such that the second magnetic bus is also in a 'UP' magnetic state. Because second selection signal 2306 is depicted as selecting the second magnetic input and because second input 2322 is in an 'UP' magnetic state, domain wall 2308 is also in an 'UP' magnetic state.
  • magnetic device 2300 will operate substantially as described above with respect to FIG. 1 .
  • FIG. 24 illustrates a logic diagram that shows the operation of the magnetic multiplexer.
  • the diagram shows that, when the first input (e.g. first input 2321 depicted in FIG. 23A ) and the second input (e.g. second input 2322 depicted in FIG. 23A ) control the first and second magnetic buses such that both magnetic buses are in the same magnetic state, the resulting domain wall will also share that magnetic state.
  • the diagram also shows that, when the first input (e.g. first input 2321 depicted in FIG. 23B ) and the second input (e.g. second input 2322 depicted in FIG. 23B ) control the first and second magnetic buses such that both magnetic buses are in a different magnetic state, the resulting domain wall will share the same magnetic orientation as whichever magnetic bus that is selected by the selection signal.
  • FIG. 25 illustrates another magnetic device configured to interact with logic components in a magnetic propagation layer 2500.
  • Illustrated magnetic device 2520 is depicted as receiving control signals 2501 and 2502 from logic component 2530 and logic component 2532 respectively, and transmitting output signal 2505 to logic component 2534.
  • FIG. 25 shows that, as is the case with other multiplexers, the magnetic device described herein can be connected to other logic elements, such as AND, NOT, OR, XOR, or other logic gates, in a logic circuit to result in a desired logic output.
  • the magnetic device might operate in accordance with other elements in the logic circuit.
  • a clock signal may be provided such that controlling the magnetization orientations of the first and second magnetic buses is performed periodically at a first rate, and such that the selection signals are provided periodically at a second rate.
  • the magnetic device may receive and send logic signals to other logic elements in the circuit. In some embodiments, such logic elements may also be magnetically implemented.
  • control signals 2501 and 2502 may include a stream of domain walls that propagate from another magnetic device, and selection signal drivers 2523 and 2524 may responsively drive selection signals 2503 and 2504.
  • selection signal drivers 2523 and 2524 may responsively drive selection signals 2503 and 2504.
  • a combination of magnetic and electronic elements may be used in the logic circuit.
  • Magnetic device 2520 can drive selection signals 2503 and 2504 based on received control signals 2501 and 2502 respectively.
  • a first selection signal driver 2523 corresponding to a first magnetic bus may receive a control signal 2501 from logic component 2530 and responsively drive a selection signal 2503 between the first magnetic bus and an output magnetic bus of magnetic device 2520.
  • a second selection signal driver 2524 corresponding to a second magnetic bus may receive control signal 2502 from logic component 2530 and responsively drive a selection signal 2504 between the second magnetic bus and the output bus of magnetic device 2520.
  • magnetic device 2520 includes independently controllable inputs 2521 and 2522.
  • Input 2521 controls a magnetization state of the first magnetic bus and input 2522 controls the magnetization state of the second magnetic bus.
  • input 2521 is depicted as controlling the first magnetic bus such that the first magnetic bus is in a 'DOWN' magnetic state and input 2522 is depicted as controlling the second magnetic bus such that the second magnetic bus is in an 'UP' magnetic state.
  • these magnetization states may change over time.
  • magnetic device 2520 may receive control signals from logic components 2530 and 2532 over time that cause output signal 2505 to be sent to logic component 2534.
  • Output signal 2505 can include a stream of domain walls that propagate along the output magnetic bus towards logic component 2534.
  • First input 2521 and second input 2522 may control magnetization states of the first and second magnetic buses independently from each other and independently from logic components 2530 and 2532.
  • inputs 2521 and 2522 may each receive signals from separate logic components or controllers, and may control magnetic orientations of the first and second magnetic buses based on the received signals.
  • inputs 2521 and 2522 may be controlled by a common controller or may be operated in accordance with logic components 2530 and 2532.
  • first input 2521 may control the magnetic orientation of the first magnetic bus at or near the same time that control signal 2501 is received by first selection signal driver 2523
  • second input 2522 may control the magnetic orientation of the second magnetic bus at or near the same time that control signal 2502 is received by second selection signal driver 2524.
  • FIG. 26 illustrates an exemplary method 2600 in accordance with embodiments of the invention, and may apply to magnetic devices described above, such as those illustrated in FIG. 21 , FIG. 22 , 23 , and/or FIG. 25 .
  • Method 2600 includes block 2602, which may be performed to provide a magnetic device comprising a magnetic propagation layer.
  • the magnetic propagation layer can include a plurality of magnetic buses configured to guide propagating magnetic domain walls along a longitudinal direction, and an adjoining region in which the magnetic buses converge.
  • the plurality of magnetic buses may include at least a first magnetic bus and a second magnetic bus having controllable magnetization orientations.
  • the magnetic buses may further include an output magnetic bus serving as an output for the stream of domain walls.
  • Method 2600 further includes block 2604, which may be performed to control a magnetization orientation of at least one of the first magnetic bus and the second magnetic bus.
  • controlling the magnetization orientation of at least one of the first magnetic bus and the second magnetic bus may include providing magnetic interconnections between at least one logic element in the magnetic propagation layer and the first magnetic bus and the second magnetic bus.
  • the at least one logic element may be configured to control the magnetization orientation of the first magnetic bus and the second magnetic bus.
  • controlling the magnetization orientation of at least one of the first magnetic bus and the second magnetic bus may include providing charge-to-spin converters corresponding to each of the first magnetic bus and the second magnetic bus.
  • the charge-to-spin converters are configured to control the magnetization orientation of the first magnetic bus and the second magnetic bus.
  • method 2600 may additionally include providing a clock signal.
  • controlling the magnetization orientation of at least one of the first magnetic bus and the second magnetic bus can be performed in accordance with the clock signal, and applying the plurality of selection signals is performed in accordance with the clock signal.
  • Method 2600 additionally includes block 2606, which may be performed to generate the stream of domain walls propagating along the output magnetic bus by applying a plurality of selection signals between the output magnetic bus and at least one of the first magnetic bus and the second magnetic bus such that each domain wall corresponds to a controlled magnetization state of either the first magnetic bus or the second magnetic bus.
  • applying each selection signal of the plurality of selection signals may include applying an in-plane current between the output magnetic bus and one or both of the first magnetic bus, such as to establish at least one current path through the adjoining region toward the output magnetic bus.
  • the plurality of magnetic buses can collectively operate as a multiplexer.
  • method 2600 may further include providing at least one other logic element in the magnetic propagation layer. The at least one other logic element interacts with the plurality of magnetic buses in accordance with a desired logic output.

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